The present invention is directed to pulverulent cementitious composition which can be used to form cements having high early strength as well as being cements of low permeability and high durability. The invention is particularly suitable for use in cementing operations involving wells in the oil and gas industry.
In using a cement, and often in certain types of cementing operations in the oil and gas industry, it is desired to have a cement which will rapidly give early high strength and/or which will have low fluid loss characteristics. In an effort to obtain ever better results, various materials such as chromium, chlorides, and the like have been included with the clinker normally used to form cements to increase the early high strength, and these additives are costly and often toxic or corrosive. Other materials, such as accelerators and plasticizers have also been added to the cement, but these have drawbacks of their own, not only in terms of cost but in terms of also being corrosive, toxic or polluting materials. For example, chloride-type accelerators, if used in cements which come into contact with metallic objects, such as the use of high early strength cements in sealing the annulus between the metal well casing and the bore hole of an oil and gas well, can act to corrode the casing.
Also, often such cements do not have a sufficiently small particle size to be utilized effectively in forming non-permeable building blocks or for squeeze cementing in oil, gas and other wells or which, regardless of particle size, do not perform satisfactorily without additives or additional processing steps. Squeeze or remedial cementing is the process of forcing a cement slurry into perforations, holes in the well casing, or cavities behind the well casing or liner. Such cementing is usually performed during the drilling and completion of a well, or in repairing or altering an already drilled well. Illustrative is the inability often to obtain the required primary cementing in squeeze cementing without first cleaning the area of the well to be cemented with water, a non-acid wash, or with an acid flush, regardless of the particle size of the cement. Also, in squeeze cementing, the cementitious material presently used does not have the low fluid loss characteristics desired.
Not only have the additive materials not given the desired results of the high early strength, but in compositions which do not utilize additives, but rely only on small particle size, satisfactory results cannot be obtained, and there is often noted irregular setting time for the cement. Such small particle size for the high early strength are shown in U.S. Pat. Nos. 3,239,472 and 4,160,674. As noted, small particle size alone does not give the desired results and often gives irregular setting times.